The present invention relates to a thin-film magnetic head with a layer-wise build-up on a nonmagnetic substrate for a recording medium which contains a magnetizable storage layer, into which information can be written along a track by perpendicular (vertical) magnetization. The magnetic head comprises a magnetic conducting body for carrying the magnetic flux, with two outer magnet legs and a further central magnet leg, wherein the poles of these magnet legs facing the recording medium, as seen in the direction of motion of the head, are arranged one behind the other and with predetermined gap widths between each other. The magnetic head is further provided with a read/write coil device, the current conductors of which extend through one of the spaces formed between the central magnet leg and one each of the adjacent outer magnet legs. Such a magnet head is known, for instance, from European Patent application No. 0 078 374 Al.
The principle of vertical magnetization for storing information in special recording media is generally known (see, for instance, "IEEE Transactions on Magnetics", vol. MAG-16, No. 1, January 1980, pages 71 to 76; DE-OS No. 29 24 013 or U.S. Pat. No. 4,278,544; European Patent Application No. 0 012 910 Al; European Patent Application No. 0 012 912 Al. The recording media to be provided for this principle, also called vertical magnetization, may be present in the form of rigid magnetic discs, flexible individual discs (floppy discs) or magnetic tape. Such a recording medium has at least one magnetizable storage layer of predetermined thickness which contains a magnetically anisotropic material, particularly of a CoCr alloy. The axis of the so-called easy magnetization of this layer is oriented perpendicularly to the surface of the medium. By means of a special magnetic head, the individual pieces of information can then be written along a track as bits in successive sections, also called cells or blocks, by appropriate magnetization of the storage layer. In practice, the magnetic flux changes, i.e., the transitions from one magnetization direction to the opposite one are generally used as the information. The bits have a predetermined extent, also designated as the wavelength, in the longitudinal direction of the track. This extent can be substantially smaller than the limit which exists with storage according to the known principle of longitudinal (horizontal) magnetization by the demagnetization. Thus, the information density in the special recording media can be increased accordingly by vertical magnetization.
The combined magnetic write and read heads known for the principle of longitudinal magnetization, i.e., heads with which the write as well as the read function can be carried out, cannot be used without problem for vertical magnetization. When using these heads, which generally have a shape similar to a ring head, although a magnetic flux conduction also desired with the principle of vertical magnetization to form a circuit closed as far as possible with low magnetic resistance can be achieved, it is difficult to generate a sufficiently strong writing field for high bit densities and a correspondingly small width of the so-called air gap formed between the magnetic poles.
One is therefore compelled to develop special magnetic write/read heads for the principle of vertical magnetization. A head suitable therefore comprises, in general, a so-called main pole, by which a sufficiently strong vertical magnetic field for changing the magnetization of the individual sections of the storage layer is generated. The necessary magnetic return can then be realized, for instance, by means of a so-called auxiliary pole which is located, as far as the recording medium is concerned, for instance, on the same side as the main pole (see, for instance, "IEEE Trans. Magn." vol. MAG-17, No. 6, November 1981, pages 3120 to 3122 or vol. MAG-18, no. 6, November 1982, pages 1158 to 1163; U.S. Pat. No. 4,287,544; European Patent application No. 0 012 912 Al).
In magnetic heads of this head type, the auxiliary pole is to serve in all cases only for the return of the magnetic flux. A possible concurrent writing of this pole may possibly be tolerated because it is always lagging the writing main pole and thereby overwrites information which may have been written by the auxiliary pole. However, in order to suppress concurrent reading of the auxiliary pole with its trailing edge at least to a large extent, the air gap formed between the two poles would have to be relatively wide in order to be able to thus ensure a far-reaching reduction of the magnetic flux density at the auxiliary pole. Gap layers of such width, however, can be realized in magnetic heads to be built-up by a thin-film technique only with difficulty.
This technique is generally known (see, for instance, "Feinwerktechnik und Messtechnik", vol. 88, No. 2, March 1980, pages 53 to 59, or "Siemens-Zeitschrift", vol. 52, No. 7, 1978, pages 434 to 437). The magnetic head shown in European Patent Application No. 0 078 374 Al mentioned at the outset also is to be manufactured by this technique.
Due to the difficulties arising with respect to concurrent reading of the auxiliary pole, the magnetic head known from European Patent Application No. 0 078 374 Al has not only two magnet legs forming a main and an auxiliary pole, but also a third, central magnet leg which is arranged between the two outer magnet legs. The ends of these, therefore, three magnet legs which face the recording medium and which each form a pole are spaced from each other by a narrow air gap, so that this magnetic head type is also designated as a double-gap magnetic head. Through only one of the two magnetic heads formed between the central magnet leg and a respective outer magnet leg extend the current conductors of a write and read coil winding, while the other space is filled with a nonmagnetic material. With this design of the known magnetic head, it should be possible to generate for the write function a magnetic field which has in the vicinity of the pole of the central magnet leg a narrow, strong maximum of predetermined polarity, while in the adjoining regions of the poles of the two outer magnet legs, a substantially wider but only weak maximum with opposite polarity follows. (See FIG. 4 of this European Patent application). It has been found, however, that this idealized symmetrical field pattern can hardly be achieved with this known magnetic head. The magnetic field formed between the poles of the one outer magnet leg and the central magnet leg rather is substantially smaller than the magnetic field of the poles of the central magnet leg and the other, outer magnet leg. This makes the field heavily asymmetrical and differs only slightly from the field pattern such as is generated by known thin-film magnetic heads with ring head-like shape, for instance, according to European Patent Application No. 0 012 912 Al and is shown in FIG. 3 of European Patent Application EP 0 078 374 Al.